1. Field of the Invention
The present invention relates to processes of removing radioactive nuclei or naturally occurring radioactive material (NORM) and, more particularly, to a process which removes radium, such as radium-226, from phosphogypsum material generated during the production of phosphoric acid and which reclaims and decontaminates gypsum.
2. Discussion of the Background
Currently, in the phosphoric acid production industry in which phosphate-ore is processed by the wet-acid process to produce phosphoric acid, the phosphogypsum slurry, often called “gyp” slurry, is pumped to large separation/settling areas where phosphogypsum solids are separated from the liquids. The liquids are then either reused or neutralized and discharged in accordance with state and federal regulations governing plant discharges. The solids remain on-site and are stored in large mound-like hills (note that within the context of the present invention, the combination of the separation/settling area and mound-like hills are referred to as “stacks”), mainly because the level of radium-226 exceeds the regulatory limits of 10 picocuries per gram (10 pCi/g) established under the National Emission Standard for Hazardous Air Pollutants, or NESHAP, 40 CFR § 60.204–60.206. Alternatively, in facilities that are situated on or very near the phosphate ore mines, the solids can be mixed with overburden and put back into the mines to reclaim the mines. These solids must be monitored while on-site and any future use of these solids is severely limited by their radium content.
In view of the foregoing, there is a continuing need for a cost-effective and environmentally friendly process which separates and recovers radium-226 from the phosphogypsum solids yielding non-regulated phosphogypsum.
Furthermore, in decontaminating or other operations in which nitric acid is used to decontaminate, treat or otherwise process material containing phosphogypsum, there is a continuing need for a process, which includes a step to neutralize or otherwise remove residual nitric acid and/or nitrates in non-regulated phosphogypsum for use in construction materials or other applications.